Acceleration and stutter? help guys :)

Went for petrol, but before hand reduced the duty by 2% to set it at 47. Warmed her up then put my foot down in 2nd and it boosted fine. Filled up with petrol, came back to work. Put my foot down in 2nd when going straight on off a roundabout and I *think* it overboosted and kicked me back. It was like a jolt/shudder and a small bang/pop from the exhaust (I think it was a bang but I might have been hearing things).

Confused, as the first day I got it back, the drive home was faultless and it was running superb with no problems like this at all :?

 

When it pops/bangs and shudders does the CEL flash?

What's the peak boost and rpm on the commander?

Andrew...

 

It doesnt flash Andrew, no.

I didnt check the peak boost and rpm. Will it still be stored after the engine is switched off, or will I have to do another run? If so, I'll do one tonight.

 

No it's not stored.

 

I've decided to do a run down of whats happened since I got her back. I apologise, its a bit long winded but will hopefully help in diagnosing further :

Once again, spec :

Full spec is :

2000 Impreza P1
Full decat 3" - 2.5" Afterburner
K&N 57i Induction Kit
Front Mounted Intercooler
Apexi PFC mapped by Andy F a couple of weeks ago
NGK PFR7B's (or 6B's, cant recall. They were the ones recommended by Andy)
Walbro 255 Fuel Pump
AP Racing clutch

* Apexi ECU mapped by Andy Forrest on Esso Supreme 97RON (they are no Shell VPower stations within 25 miles of where I live, but Tesco are set to release the 99RON up here soon, so it will be back to Andy to be mapped on that when available)

* Andy suggested I re-attach the engine tray underneath, as when the FMIC was being fitted, the tray looks like its been cut back to suit. The downside being travelling at over 55mph forces the tray to hang down and flap on the ground due to the pressure and air flow. The tray is being removed tomorrow, rather than re-attached again at the centre. This was recommended by a few people on P1woc.

* On way home, stopped and filled up with BP Ultimate 97RON as there were no Esso, unfortunately.

* Had a good few sprints of acceleration, including a turn left at a roundabout and floored it. Acceleration was amazing, and no hint of boost problem at all (obviously I would have been unaware at this stage of any anyway)

* The next day, I took my mate out in it. Cant remember the quantity of petrol in the tank, but definitely less than half. Took the 3rd exit from a roundabout (full right turn) and put my foot down in second. Wham, kicked back as if I'd redlined, only far too early. Changed up a gear, 3rd, 4th and 5th all superb speed and pulled amazingly. Not a sausage wrong after that.

* A day later I believe, me and my girlfriend went for some food and the petrol light was on. Took a left at a junction and put my foot down in second. Wham, kicked back again. Changed to 3rd gear and accelerated and it felt like it was trying to force too much air through the exhaust system. It popped a little and contined on, a bit sluggish, however, kind of laggy.

* Got home, had the food and decided to go for some petrol and test the car (after a few threads I'd read on similar problems). However, started car and after about 15 seconds it died on me. I started it up again, and it coughed a bit and then conked out again. Tried again, same. It was at this point I thought I'd done something seriously wrong.

* I decided to use my girlfriends car (an Evo 6, oh the shame) to go for a bit of petrol in a can. Filled up with about £5 worth, which was all I could fit in. Came home, filled up the P1 as best I could. Gave it a couple of minutes and started it up. Spot on. Started fine. Went for £20 worth of more petrol and came home and parked up.

Now this was alarming, because the petrol light must have been on for about 5 minutes, tops. Before the map and modifications, including the Walbro fuel pump, the light could stay on for a LOT longer, as a lot of people will know. It really confused me as to why it had run out of petrol so quickly after the light had came on.

* At the weekend, I took the step of trying to protect my K&N Induction kit from the rain, as recommended by Andy. I have open meshed 22B bonnet vents on the car, so any water could easily have been taken in by the 57i. I used the original blanking plate so now its protected. However, water could have gotten in during the time it wasnt fitted.

* Found out today that the sock filter on the Walbro Fuel pump is from the new pump itself, yet I've now been told its best to use the original sock filter.

* Took car out at lunch time for some petrol. Accelerated in 2nd gear. Boosted to around 1.3bar and didnt kick back. Filled up with petrol, drove back to work. Went straight on at a roundabout, upon exiting I put my foot down in 2nd. Wham, kicked back, shame I didnt manage to check the boost figure. I've just found out now that I can check the peak figures from the latest drive using the Apexi Controller handset, so I'll take it out later and have a play around.

Now its still doing the same thing on occassion. Not all the time, but on occassion, and usually in 2nd gear. With the above information, I've got into my head various suggestions from forum boards and people's takes on the situation :

* Overboosting

* Fuel Starvation

* Fuel Surge

* Maf failing

* Fuel Pump - Position of?/sock filter being newer version, not original

* Coil Packs

* Boost solenoid

* Spark plugs not gapped correctly

* Injectors not up to the job (440's)

* Hoses not connected properly

* A number of other things.


Its good to have a collection of possible problems and symptoms etc, but I'd rather know the route of the problem right away than having to check the spark plugs and all the fittings etc etc and not knowing if changing things will make any difference. Its one of those impossible questions, really, as without seeing the car and how its running, you dont know what it is. Thats why I've tried to break things down above as to give more clues in to what could be going on.

Many thanks to Andrew and everyone who's tried to help. I hope the information above adds to your thoughts.

 

For what it's worth, that sounds exactly like my car... :roll:

But I just put mine down to fuel surge, and intended on fixing this as the cure...

 

Annoying isnt it? :x

I filled up with petrol, and it still did it.
Going to do as Andrew said and run some tests later for peak figures. Then try and set the boost to the 1.2bar map and see what that does.

 

If it's a sharp cut in power then it's most likely fuel cut, what we need to establish is what is causing it, it's not necessarily as obvious as you may think.

If your pump is fitted with the filter than was supplied as part of a fitting kit then throw it away and fit a Subaru one, this needs to be done anyway regardless of whether it's causing a problem.

If the car is still cutting with a full tank of fuel then I doubt it's starvation unless there is a fault in the pump.

MY99/00s are usually very good ignition wise, although with the Apexi there can be grounding/signal quality issues with the crank sensor so it's worth cleaning that and checking the connectors/wiring.

Plugs should be PFR7Bs but worth checking that they are gapped correctly 0.7mm should be OK at that boost on a good MY99/00 coilpack.

Usual checks of earthing points, battery connections etc.

Set the commander up to display RPM/Boost/Knock/Inj Duty/Airflow and check the maximums after the car exhibits the problem, keep a close eye on the Tacho/Boost guage and CEL also (may need a passenger to help).

440cc injectors should be fine with your setup.

I suspect it's overboosting but we need the data to be sure.

Andrew...

 

Cheers. How do I set up the commander to display all that? I know I can display two on the monitor at the same time, but I'm not that familiar with it in a lot of detail as yet.

From the main menu, I select monitor, then I have the selections and I can pick two from the list. Or should I be going to another part of the controller?

lol @ keeping an eye on everything. I got cross eyed just reading what I should be watching!
No probs though, shouldnt be too bad. I dont actually think the CEL is wired to show the knock? Well, it might be, but I havent seen it occur yet.

 

Go to the top level menu: monitor/settings/etc.

Select monitor and press next

The next screen offers you 1, 2, 4, 8 or Map Trace.

Scroll down to 8 and press next then choose the items I suggested.

Pressing the up arrow will show the maximums values,
Down arrow will return to the live display,
Right arrow will clear the maximums.

Andrew...

 

Excellent Andrew. What a star you are.

So I'll choose these, then take the car on a run until it hits the limiter which doesnt exist then I can check the maximum peak settings and that will hopefully inform me (or you) if the car is overboosting or any other potential problems. Cool 8)

Sounds good. I'll do this when I get home

 

Ok guys, I took the car out with just under half a tank of petrol.

Turned left at a junction, put my foot down in 2nd and got these peak figures on the Apexi controller handset :

Duty : 75.3
Revs : 4986
Temp : 61deg
Air Flow : 4345
Boost : 1.31kg/cm sq
Knock : 16
Water Temp : 94 deg

The car didnt stutter or hesitate at all. Was fine.

I did another couple of tests. Took a right turn at a junction, and on a long straight and private road (actually being serious too) I put my foot down in 2nd gear again and it hesitated and hit the invisible limiter as though it had overboosted. Figures :

Duty : 54.1
Revs : 4107
Temp : 45deg
Air Flow : 3985
Boost : 1.19kg/cm sq
Knock : 6
Water Temp : 91 deg

so it cant have been overboosting, surely, at 1.19?

I went to the bottom of the road, did a right hand U turn and did the test again with the same outcome. Figures were almost the same, except boost :

Boost : 1.06kg/cm sq

Hmm, seems like it could be a fuelling issue perhaps? Like I said though, I had just under half a tank full.

On the way home I was on a long stretch of open road, so accelerated in 2nd and it boosted to 1.34bar with no problems at all. That was from no turning or junctions.

Also did a left hand turn at a junction and accelerated again, no problems. Really confused.

Hope this all helps with the diagnosis

 

Fuel pick up is on the RHS of the tank, so if the sock filter isn't submerged enough then when going right the fuel will move to the left and away from the pick up.

 

lol

has pump filter not come off

 

Just edited your post down to the bare bones , and compare with what Jim has said...

Think you've answered your question...?? Maybe..??

 

Just to add also, is if you actually look underneath your car, (as I have been now for quite sometime on my own :roll: ), and look at the shape of the fuel tank, you will see that the bottom half of the tank is actually divided into 2 sides by the 'hump' over the exhaust, which runs down the middle...

The pick up is one one side only...

 

And it doesn't take much to throw fuel from that side over to the other during cornering :shock:

 

Indeed. I'm pretty sure it could be a fuelling issue. I really need to remove the sock filter and refit the original which was not put on when the fuel pump was installed. In all honesty, it must be common sense to put on the sock filter that came with the Walbro pump rather than use the original. So I have no qualms with the garage using the uprated one, even though it was the wrong choice.

Surely having just under 1/2 tank would stop the chance of the fuel situation happening, though? Unless it does have something to do with the pump/filter and its situ.

Hmm...

From what I've described, can we elimate the chance of it being overboost?
What else can we rid from the list? It could still be spark plugs, right? Although would this boost issue still be evident in all gears if it was the plugs and/or leads, as it only appears to be 2nd gear - which is probably when the fuel is being thrown through at the most ferocity?

 

The filter that comes with the walbro isn't uprated in anyway, its made exactly like the OEM one just smaller, hence why it doesn't sit in the fuel as deeply.

 

But this could still make a difference to the scenario, in theory, Jim? Thanks for the replies and information guys